1. Field of the Invention
This invention relates to diamond cutting members and, more particularly, to a technology of simply manufacturing a diamond cutting member at low cost utilizing a synthetic diamond whose surface {112} or its vicinity is used as a raked face.
2. Description of the Related Art
An attempt has heretofore been made to provide a diamond cutting member wherein a raw material such as a single-crystal diamond, formed with a cutting edge and a raked face, is integrally mounted on a given holder such as base metal, a shank or the like for use in cutting work. Patent Publications 1 and 2 disclose a diamond cutting tool and a diamond cutting chip, respectively, each representing such an example mentioned above, which have been suitably used for mirror-like finishing work on soft nonferrous metal such as aluminum and copper alloy or the like. For such diamond, it has heretofore been proposed to use synthetic diamonds (refer to Publications 3 and 4). In general, the synthetic diamond has less wear resistance than that of a natural diamond but less variation occurs in individual synthetic diamonds with stable quality (wear resistant performance).
The synthetic diamond has hexahedral shapes which basically has six surfaces {100}, i.e., a cubic or a rectangular solid with adjacent surfaces extending on planes perpendicular to each other. FIGS. 9(a) and 9(b) show such synthetic diamond. FIG. 9(a) shows the synthetic diamond 10, taking the form of a simple rectangular solid, which has six flat surfaces 12 expressed as surfaces {100}. The synthetic diamond 14, shown in FIG. 9(b), takes the form of a shape having chamfered flat surfaces 16 formed on corners of the synthetic diamond 10. The chamfered flat surfaces 16 occur due to a condition under which the synthetic diamond 14 is manufactured. In the present specification, the synthetic diamond 10 will be described as involving the synthetic diamond 14 having such chamfered flat surfaces 16.
Further, a symbol “{. . . }”, described above, is a mirror index representing a crystal surface whose atoms are arrayed in a fixed arrangement. In case of diamond, as shown in FIG. 12, besides the surface {100}, a surface {111} and a surface {110} have been generally known. The natural diamond often has a basic configuration in the form of octahedral body or a dodecahedron. The octahedral body includes all surfaces formed of the surfaces {111}, and the dodecahedron includes all surfaces formed of the surfaces {110}. In FIGS. 12(a) to 12(c), all of views on a left side represent solid models illustrating crystal surfaces, and views on a right side show arrangements of the atoms on each crystal surface.
If the synthetic diamond 10 is used as a cutting member, processing the synthetic diamond 10 is difficult. With this in mind, as shown in FIG. 10(a), for instance, one of the surfaces {100} is used intact as a raked face 20 and the synthetic diamond 10 has a front distal end formed with a front clearance face 22 with a ridgeline serving as a cutting edge 24 at which the raked face 20 and the front clearance face 22 intersect each other. As shown in FIG. 10(b), for instance, the cutting edge 24 is used for achieving turning machining or the like to perform cutting work on an outer circumferential surface of a columnar workpiece 30 during a rotation thereof about an axis. This is accomplished by causing both component members to axially move relative to each other with the cutting edge 24 being pressed against the outer circumferential surface of the workpiece 30.
Such synthetic diamond 10 is mounted on a shank (not shown) at a distal end thereof for use as a cutting tool which is axially fed relative to the workpiece 30 in a manner as shown by a whitened arrow in FIG. 10(b). In addition, the synthetic diamond 10 has lateral clearance faces 26 formed on both sides of the front clearance face 22 depending on need. Moreover, the front clearance face 22 is preferably ground for removal to be slanted at a given clearance angle.
In the meanwhile, the surface {100} has relatively dense atoms, enabling the raked face 20 and the front clearance face 22 to be obtained with excellent wear resistance. The cutting edge 24 is structured with the ridgeline of the single-crystal synthetic diamond 10. This ridgeline results from a surface indicated by a shaded area in FIG. 9(a), i.e., the surface {110} that is ultimately minimized and substantially has the same wear resistance as that of the surface {110}. Thus, the ridgeline, i.e., the cutting edge 24 can be regarded as the surface {110}. Accordingly, the synthetic diamond 10 can have excellent wear resistance against a back component force acting in a direction perpendicular to the cutting edge 24 and a main component force (see FIG. 10(b)), but is weak in a direction parallel to the cutting edge 24, i.e., against a load acting in a direction along a feed component force. When feeding the cutting edge 24 along an axial direction of the workpiece 30 to perform turning machining as shown in FIG. 10(b), adequate wear resistance cannot be obtained.
Meanwhile, an attempt has heretofore been made to provide a synthetic diamond having a surface, inclined from a surface {100} forming an outer circumferential side face of the synthetic diamond to a surface (111) at an inclined angle of approximately 35°16′, i.e., a surface {112}, which is used as a raked face (see Patent Publication 5). The surface {112} is a crystal surface appearing in a position shown in FIG. 13 on a left side thereof and has an atomic arrangement shown on a right side of FIG. 13. This is geometrically obtained from a crystal structure of the diamond and its presence has been confirmed even on an X-ray analysis and Nomarski analysis. The surface {112} has hardness next to that of the surface {111}, and excellent wear resistance in a combined effect of the surface {111} or its vicinity being formed in the front clearance face.
Patent Publication 1: Japanese Patent Application Publication 2-145201
Patent Publication 2: Japanese Patent Application Publication 2000-107912
Patent Publication 3: Japanese Patent Application Publication 60-16306
Patent Publication 4: Japanese Patent Application Publication 2002-254212
Patent Publication 5: Japanese Patent Application Publication 3-208505